This invention relates to thermocouple devices. More particularly, the invention relates to a thermocouple device comprising a two-point, spring-loaded probe with replaceable tips.
Measurement of high temperature solid materials, such as, for example, the measurement of the temperature of hot metal ingots, is conventionally carried out using pointed thermocouple elements. These elements are, preferably, spring loaded to permit the user to engage the metal ingot with the measurement device using sufficient force to penetrate any oxide layer on the ingot. Typical of such a two-point spring-loaded probe is the device shown in Halstead U.S. Pat. No. 2,973,397. The probe is usually provided with pointed ends to facilitate pushing or driving the probe into the hot ingot to be measured. It is not uncommon to construct a probe in such a manner as to permit its being driven into the ingot by an external force. Alternatively, such a force could take the form of a spring-loaded impact device such as shown in Vollrath U.S. Pat. No. 2,405,076.
In any event, it will be appreciated that repeated engagements of such ingots or other metal objects will tend to blunt or bend the pointed elements, with the result of unreliable, inaccurate readings and/or frequent replacement of the elements, unless such elements are sufficiently durable or protected by rugged heat resistant structures. However, attempts to ruggedize and to increase the useful life of thermocouple elements have heretofore resulted in structures that tend to reduce the response time and accuracy of the thermocouples because of the increase in the mass and heat sinking effect of such structures.
For example, encasing the thermocouple junction within the pointed end of a steel probe results in a reduction in the response and accuracy of the device with the increase in the temperature of the junction being slow and gradual after the steel probe is placed in contact with the object under test. For example, a junction encased in such a steel probe might require as much as two and one-half minutes to reach its final temperature reading when measuring a 600.degree. F. temperature in a 3/16 inch thick aluminum plate.
One attempt to increase the response time of the thermocouple while ruggedizing the device sufficiently to provide consistent temperature readings over extended periods of repeated use involves the use of two closely spaced relatively short thermocouple elements separated by a heat resistant insulating material. Such a device is described and claimed in Feichter et al U.S. Pat. No. 4,101,343.
However, in every instance, repeated use of the various devices tends to result in sufficient wear on the end or tip in contact with the hot metal so as to require replacement of the thermocouple element.